Process for regenerating resin-bonded foundry sand

ABSTRACT

Resin-bonded foundry sand which forms part of a mould and cores that have been used for the manufacture of castings, are regenerated by depositing the whole sand mould together with its hot castings and any sand cores into a rotating vessel and tumbling these materials in the vessel during a time period sufficient to ensure that the sand mould and cores are broken down to discrete particles and the resin of the sand particles is burned away by spontaneous inflammation and combustion due to heat transfer between castings and sand. An apparatus for effecting this regerenation process comprises essentially a rotatable drum with appropriate inlets and outlets.

United States Patent [191 Vissers et a1.

[ Mar. 18, 1975 PROCESS FOR REGENERATING RESIN-BONDED FOUNDRY SAND Inventors: Bastiaan Vissers, Heemstede, Nr.

Glipperdreef; Willem Teunissen,

Amstelveen, Nr. Buyschenstein, both of Netherlands Filed: Feb. 16, 1973 Appl. No.: 333,409

Foreign Application Priority Data Feb. 16, 1972 Netherlands 7201998 US. Cl 164/5, 164/131, 241/DIG. 10 Int. Cl 822d 29/00 Field of Search 164/5, 76, 131, 132, 269,

References Cited UNITED STATES PATENTS Bennington 164/269 X Andrews 164/5 X l/l93l 1/1958 FOREIGN PATENTS 0R APPLICATIONS 1,125,757 8/1968 Un it d lfingdom Primary Examiner-Francis S. Husar Assistant Examiner-John E. Roethel Attorney, Agent, or Firm-John P. Snyder ABSTRACT Resin-bonded foundry sand which forms part of a mould and cores that have been used for the manufacture of castings, are regenerated by depositing the whole sand mould together with its hot castings and any sand cores into a rotating vessel and tumbling these materials in the vessel during a time period sufficient to ensure that the sand mould and cores are broken down to discrete particles and the resin of the sand particles is burned away by spontaneous inflammation and combustion due to heat transfer between castings and sand. An apparatus for effecting this regerenation process comprises essentially a rotatable drum with appropriate inlets and outlets.

11 Claims, 2 Drawing Figures 1 PROCESS FOR REGENERATING RESIN-BONDED FOUNDRY SAND This invention relates to resin-bonded foundry sand and more in particular to a process and apparatus for regenerating such foundry sand when it forms part of a mould and cores that have been used for the manufacture of metal castings.

Moulds and cores of crystal sand bonded by a thermosetting synthetic resin have found a widespread use for the manufacture of metal castings in recent years. The thermosetting resin therein may be e.g., a furane resin made by curing furfuryl alcohol at 250C in the presence of a phosphoric acid catalyst, or alternatively a ureaformaldehyde or phenol-formaldehyde resin. Such resins have the advantage of providing a satisfactory bonding strength and resulting in moulds and cores that retain their forms during utilisation.

A disadvantage of the aforementioned synthetic resins is, however, that the foundry sand can hardly be regenerated after use and after removal of the castings.

This used foundry sand comprises a non-neglectable amount of synthetic resin in the form of hard films around the sand grains and such films are extremely difficult to remove. The most widely practised method at the moment is to grind the moulds and cores after use to form discrete particles and then to blow these sand particles many times under high pressure against an abrasion-resistant wall. Thanks to collision against this wall and thanks to mutual friction of the sand particles, the resin films around the sand grains are broken then and are partially or completely pulverised, whereupon the resulting fines and grit are removed from the sand by means of suction. This process, however, will consume much energy since many collisions are needed to remove the whole resin film from a sand particle. Moreover, this process has a deleterious effect on the sand grains resulting in the fact that only 50 percent of the grains is suitable for re-use in moulds and cores.

During experiments which led to the invention, it has now been found that the resin films around the sand grains may be removed effectively by burning them away and that the temperature required for spontaneous inflammation and combustion of the resin films may be obtained by heat transfer with hot castings.

An object of the invention is to provide a process of regenerating foundry sand which overcomes the above disadvantages.

Another object is to provide a process of regenerating foundry sand which consumes less energy.

A further object is to provide a process for regenerating foundry sand which has for its result that a high percentage of the regenerated sand grains can be re-used in moulds and cores. v

Still another object is to provide a process for regenerating foundry sand whereby the resin films around the sand grains may be removed effectively by burning them away.

A further object is to provide a process for regenerating foundry sand wherein the sand is regenerated by means of hot castings. A still further object is to provide a process for regenerating foundry sand wherein the sand after regeneration together with hot castings is cooled down efficiently to ambiant temperature.

The invention has for a further object to provide an apparatus for regenerating foundry sand which is capable of effecting the above-mentioned process.

A further object of the invention is to provide an apparatus for regenerating foundry sand which is capable of effectively removing the resin films from sand grains bonded with synthetic resin.

Still another object is to provide an apparatus for regenerating foundry sand which has for its result that a high percentage of the regenerated sand grains may be re-used in moulds and cores.

A further object is to provide an apparatus for regenerating foundry sand wherein the sand is regenerated by means of hot castings.

A still further object is to provide an apparatus for regenerating foundry sand wherein the sand after regeneration together with hot castings is cooled down efficiently to ambiant temperature.

Accordingly, the invention provides a process of regenerating foundry sand bonded with a thermosetting synthetic resin and forming part of a mould and cores (if necessary) that have been used for the manufacture of castings. In one of its aspects this process comprises the steps of depositing the whole sand mould together with its hot castings and any sand cores into a rotating vessel and tumbling these materials in that vessel during a time period sufficient to ensure that the sand mould and cores through contact with the hot castings are heated to such a temperature that the synthetic resin is removed from the sand by spontaneous inflammation and combustion and the sand mould and cores are completely broken down to discrete sand particles.

Further, the invention provides an apparatus for carrying out the aforementioned regeneration process. In one of its aspects, this apparatus comprises a vessel in the form of a horizontal cylindrical drum which has an inlet for castings and sand moulds at one end and an outlet for castings and regenerated sand at its other end, said drum being mounted for rotation about its longitudinal axis, and being provided with one or more profile bars at the inner side of its cylindrical walls as well as with one or more burner tubes and conduits for supply of fuel gas and/or conduits for supply of an oxy' gen-containing gas at its inside.

The effect of the vessel or rotating drum is two-fold. On one hand, the sand moulds and sand cores are broken down during the tumbling step to discrete sand particles thanks to the castings which serve the function of grinding bodies. This has the advantage that only a minimum of energy is needed for grinding purposes because the bonding forces of the synthetic resin decrease at the temperatures existing in the drum. On the other hand, an intense heat transfer between the hot castings and the sand particles is taking place during this tumbling step and thanks to such heat transfer the sand is heated at a temperature of about 400C by the hot cast ings. Such a temperature is sufficient to ensure a spontaneous inflammation and combustion of the synthetic resin films around the sand grains. When the vessel has been charged in a normal way, the synthetic resin at the surface of the sand particles is in contact with sufficient air or oxygen to ensure that the combustion is complete but, if desired, an additional quantity of air or oxygen may be introduced into the vessel through an appropriate conduit. Should the heat supplied by the castings be insufficient to maintain the temperature during a'sufficient period of time at the required level for complete combustion of the resin films, then an additional quantity of heat may be added by means of one or more burners fed with gas or oil. The sand grains are regenerated and cleaned completely in this way and the gaseous combustion products comprise substantially exclusively carbon dioxide and water vapour. Further, the sand is nearly completely dried during this tumbling step and this is an additional advantage. The resulting products may be discharged together and thereafter be separated and cooled individually. The sand is suitable then without any further operational steps for re-use in making moulds and cores.

Alternatively, the resulting combination of hot castings and hot, regenerated sand may be passed as a whole to a cooling drum for further cooling of the products to ambiant temperature, whereupon the components are separated. Such a cooling drum may be of the type disclosed in British Pat. No. 1,125,757 and comprises a vessel in the form of a rotatably supported, horizontal drum having an inlet for castings and sand at one end and anoutlet for cooled castings at its other end. A portion of the cylindrical wall of the drum has been perforated and may cooperated with an outlet for separating and discharging cooled sand. The

mixture of castings nd sand is tumbledarggndjn such such drum whilst a stream of cold air is sucked through and a water spray, if necessary, is i troduced into the drum. The air and water take up heatfrom the tumbling materials whereby the water is evaporated and thereafter they are discharged together from the drum. Thanks to this air passage, to the evaporation of added water and also to heat transfer with the surrounding atmosphere, sufficient heat is removed to cool the castings and sand to ambiant temperature. The sand is separated then from the castings by means of the perforated portion of the drum wall and discharged through the cooperating sand outlet whilst the castings are discharged through the outlet at the other end of the drum. In this way, a good cgoling effect is achieved. The resulting sand is again completely free from synthetic resin and may be re-used without any further operational steps for making moulds and cores. A further advantage of the cooling drum is, moreover, that any residual concentration of phosphoric acid in the sand (derived from the resin catalyst) may be neutralised by means of a slightly alkaline pH of the water spray introduced into the drum. V W A The invention is illustrated by the drawing which shows an embodiment of the invented apparatus by way of example.

FIG. I is a longitudinal section through this embodiment.

FIG. 2 is an elevation of this embodiment on a smaller scale, when it has been coupled with an apparatus for cooling castings and sand.

The apparatus of FIG. 1 comprises a vessel in the form of a cylindrical drum 1 supported horizontally on rollers 2 for rotation around its longitudinal axis. The cylindrical wall 3 of the drum is closed over its entire length and has at its inner side a number of profile bars 4 extending parallel to the longitudinal axis of the drum. The drum has an end wall 5 provided with a central inlet opening 6 at one of its ends. A stationary inlet chute 7 is projecting through opening 6 into the drum and has a branch tube 8 which may be connected to an 4 d hi hm be ked i h 2. 2- f d s red,

the lid 11 maybe 5 sliding lid. A burner tube 13 having vided with a valve 18. This conduit may be connected with a source of oxygen-containing gas such as oxygen,

air or oxygen-enriched air (not shown).

The apparatus as described is operating as follows:

During operation, the drum-l is rotating with the aid of suitable driving means (not shown). Partially cooled mould flasks which comprise a sand mould with one or more fresh castings and, if necessary, sand cores contained therein, are advanced to the drum and opened, whereupon the whole contents of the mould flasks that is castings plus sand mould plus any sand cores is deposited into the drum through inlet chute 7. This material remains for some time in the rotating drum and is advanced gradually therein from its inlet end to its discharge end. Thanks to the rotation of the drum 1 and with the aid .of the profile bars 4, the castings and sand moulds are continuously tumbled and mixedwhereby the castings have the function of grinding bodies to break the sand moulds and cores down to discrete sand particles. Subbling action of the drum, however, an intense heat transfer is taking place, and the temperature of the sand will be raised thereby to an average value of 400C. At this temperature, when all sand grains are in motion, the resin films around the sand grains as well as any free resin particles are capable of spontaneous inflammation and combustion. When the drum has not been overcharged, there will be sufficient air in the drum to sustain the combustion but nevertheless and whenever required, additional air or oxygen may be :supplied through conduit 17. The resulting combustion apparatus (not shown) for removal by suction of com- 5 bustion gases formed in the drum during operation.

The drum 1 is covered at its other end by a stationary gases may be removed by suction through branch tube 8.

In the case that a relatively large amount of iron and a relatively small amount of sand is present in the drum, the iron is capable of supplying sufficient heat to sustain the combustion of the resin from the mould sand and this resin will be burned away completely. In the other case that a relatively small amount of iron is present, however, there will be transferred only a limited amount of heat from the iron to the sand and in that case, an additional amount of heat should be supplied by means of the burners 14. When conduit 15 has been connected with a fuel source and conduit 17 has been connected with a source of oxygen-containing gas, then heat is supplied by means of the burners l4 and an excess of oxygen is introduced simultaneously through conduit 17. The profile bars 4 serve to take up the'sand each time and this sand when released falls down through the burner flames which ensures a good combustion of the resin in a short period of time.

Thanks to the high temperatures existing during combustion of the resin, all moisture present in the mould sand will also evaporate. This moisture in the form of water vapour is removed from the drum together with the gaseous combustion products by means of suction through branch tube 8.

The drum may be operated continuously or discontinuously. During discontinuous operation, the lid 11 is kept closed (dotted lines) and the contents of the drum are kept therin during a period of time sufficient to en sure that all synthetic resin of the mould sand has been burned away completely, whereupon the lid 11 is opened and the whole contents of the drum, that is castings plus sand, are discharged through the outlet 10. During continuous operation, the lid 11 is always opened (or is ommitted) and the amount of material introduced into the drum is selected with regard to the length of the drum in such a way that the sand will be freed completely of resin when it has passed the whole drum. In this case too, the castings plus sand are discharged through the outlet 10. In both cases, the resulting sand is completely colourless due to the absence of resin and carbon particles.

The mixture of hot castings and hot sand may be processed further in various different ways. Thus, the mixture may be seperated by means of a perforated conveyor belt, whereupon the sand falling through the perforations is cooled and the castings are passed further on the belt. As an alternative, perforations may be provided in the outlet in order to separate the sand from the castings.

Another possibility is that the resulting combination of hot castings and hot sand is cooled together in a cooling drum as disclosed in British Pat. No. 1.125.757 and then separated. This possibility is shown in Figure 2.

At the left side of FIG. 2 is shown the same apparatus as in FIG. 1, that is a cylindrical drum 1 rotatably supported on rollers 2 and provided with a stationary inlet chute 7, with suction branch 8 and a stationary end wall 9 with outlet opening 10, as well as a burner tube 13 with flame apertures 14 and an oxygen conduit 17. The lid 11 is absent in this case so as to allow a continuous operation of the drum 1.

This drum 1 is coupled to a cooling drum (at the right hand side of FIG. 2) comprising a vessel in the form of a cylindrical drum 19, supported in horizontal position on rollers for rotation around its longitudinal axis. The drum 19 has an end wall with central inlet opening 22 at one end and a stationary inlet chute 23 connected with the outlet 10 of the drum 1 is projecting inwardly through this opening 22 into drum 19. The inlet chute 23 is provided with a branch tube 24 which may be connected to an apparatus for removal of air and water vapour by means of suction.

The drum 19 is covered at its other end by a stationary end wall 25 which has a central opening 26 for re ceiving a stream of cold air by suction and which has an outlet 27 for discharge of cooled castings.

The cylindrical wall 28 ofthe drum 19 has a circumferentially perforated portion 29 for separating cooled sand from the drum and non-perforated portions 30 and 31 on either sideof it. The perforations in the perforated portion have a diameter of e.g., 20 millimeters portion is closely surrounded at the lower side of the drum 19 by a stationary outlet chute 32 for discharge of cooled sand.

The portion 31 of the drum wall need not always be present and in that case the perforated portion 29 will extend until the discharge end of the drum. The portion 30 near the inlet end of the drum 19 is needed, however, for a good contact between castings and mould sand and it should have an axial length of at least half the axial length of the perforated portion 29. Further, the axial length of the perforated portion 29 may be varied between certain limits by means of two slidable sleeves 9 mounted around the drum wall for covering part of the perforated portion 29.

A conduit 34 with spray apertures 35 has been provided within the drum 19 and is connected with a conduit 36 leading to the outside of the drum. This conduit 36 bearing a valve 37 may be connected with a source of water (not shown) and the water from this source is preferably made slightly alkaline.

During operation of the apparatus of FIG. 2, drum 1 has the same function as described above. The castings and hot sand leaving this drum are continuously fed to the rotating drum 19 through outlet 10 and inlet 23. In this drum 19, the castings and sand are again tumbled and mixed and also advanced in the direction of the discharge end. During this tumbling movement, the castings are again in intimate contact with the sand so as to ensure a good heat transfer. A stream of cold air is passed by suction through the drum 19 via opening 26 and branch tube 24 and this stream of cold air takes up a major part of the heat from the castings and sand. Further, a water spray (not always necessary) may be introduced through conduit 31 into the drum. This water spray will absorb part of the heat from the sand and the castings and will then evaporate whereupon it is removed in vapour form by suction through branch tube 24. Another part of the heat from the sand and castings is removed by heat transfer through the drum wall to the surrounding atmosphere.

When the combination of castings and sand passes the perforated portion of the drum wall, sand is gradually separated from the castings and discharged through perforated portion 29 and outlet 32. This sand is completely dried and drastically cooled. The castings proceed further in the direction of the discharge end of the drum and leave the drum through the outlet 27. When leaving the drum, the castings are already substantially cleaned so that any after-treatment by means of shot blasting may be shortened and the step of beating out the cores (if any) is not necessary.

Thanks to the treatment in the cooling drum, the temperature of the sand and castings may be lowered to about the ambiant temperature. If the water spray has been made slightly alkaline (having a pH of about 8) then any phosphoric acid residue in the sand (derived from the catalyst of the synthetic resin) is also neutralised.

Thanks to the apparatus of FIGS. 1 and 2 and the process effected thereby, the sand grains may be freed completely from synthetic resin and the size and shape of the sand grains are not substantially affected. The sand may be re-used immediately for making moulds and cores. Further, the sand is completely dry. A further advantage is that the moisture-free sand may be passed over a magnet in a layer of e.g., 5 millimeters, in order to remove any iron particles from it. The completely dried sand grains will not have any tendency of agglomeration during storage.

We claim 1. A process of regenerating foundry sand bonded with a thermo-setting synthetic resin and forming part of a mould and cores that have been used for manufac@ turing castings, comprising the steps of depositing said whole sand mould together with its hot castings and any sand cores into a rotating vessel and tumbling such materials in that vessel during a time period sufficient to ensure that the sand mould and cores through contact with said hot castings are heated to such a temperature that'the synthetic resin is removed from the. sand by spontaneous inflammation and combustion and the sand mould and cores are completely broken down to discrete sand particles.

2. The process as claimed in claim 1, wherein the materials within said vessel are passed through flames in order to ensure a complete combustion of synthetic resin.

3. The process as claimed in claim 1, wherein an oxygen-containing gas is supplied to the materials within said. vessel to ensure a good combustion of synthetic resin.

4. The process as claimed in claim 1, wherein any flue gases and water vapor resulting from combustion of synthetic resin are moved from said vessel by suction.

5. The process as claimed in claim 1, wherein a combination of hot castings and hot, regenerated sand re sulting from said tumbling step is separated into its components and the separate components are cooled individually.

6. A process of regenerating foundry sand bonded with a thermo-setting synthetic resin and forming part of a mould and cores that have been used for manufacturing castings, comprising the steps of depositing said whole sand mould together with its hot castings and any sand cores into a first rotating vessel and tumbling such.

tion of hot castings and hot, regenerated sand as resulting from said tumbling step into a second rotating vessel and tumbling such materials in that second vessel during a time period sufficient to ensure that the castings and sand are cooled down to ambiant temperature, and thereupon separating the resulting combination of castings and sand into its components.

7. The process as claimed in claim 6, wherein the materials within said first vessel are passed through flames in order to ensure a complete combustion of synthetic resin.

8. The process as claimed in claim 6, wherein an oxygen-containing gas is supplied to the materials within said first vessel to ensure a good combustion of synthetic resinf 9. The process as claimed in claim 6, wherein any flue gases and water vapor resulting from combustion of synthetic resin are removed from said first vessel by suction.

10. The process as claimed in claim 6, wherein the materials within said second vessel are tumbled under a water spray.

11. The process as claimed in claim 6, wherein the materials within said second vessel are tumbled under a water spray and wherein said water spray has a slightly alkaline pH value for neutralising any phosphoric acid as present in said regenerated sand. 

1. A PROCESS FOR REGENERATING FOUNDRY SAND BONDED WITH A THERMO-SETTING SYNTHETIC RESIN AND FORMING PART OF AMOULD AND CORES THAT HAVE BEEN USED FOR MANUFACTURING CASTINGS, COMPRISING THE STEPS OF DEPOSITING SAID WHOLE SAND MOULD TOGETHER WITH ITS HOT CASTINGS AND ANY SAND CORES INTO A ROTATING VESSEL AND TUMBLING SUCH MATERIALS IN THAT VESSEL DURING A TIME PERIOD SUFFICIENT TO ENSURE THAT THE SAND MOULD AND CORES
 2. The process as claimed in claim 1, wherein the materials within said vessel are passed through flames in order to ensure a complete combustion of synthetic resin.
 3. The process as claimed in claim 1, wherein an oxygen-containing gas is supplied to the materials within said vessel to ensure a good combustion of synthetic resin.
 4. The process as claimed in claim 1, wherein any flue gases and water vapor resulting from combustion of synthetic resin are moved from said vessel by suction.
 5. The process as claimed in claim 1, wherein a combination of hot castings and hot, regenerated sand resulting from said tumbling step is separated into its components and the separate components are cooled individually.
 6. A process of regenerating foundry sand bonded with a thermo-setting synthetic resin and forming part of a mould and cores that have been used for manufacturing castings, comprising the steps of depositing said whole sand mould together with its hot castings and any sand cores into a first rotating vessel and tumbling such materials in that first vessel during a time period sufficient to ensure that the sand mould and cores through contact with said hot castings are heated to such a temperature that The synthetic resin is removed from the sand by spontaneous inflammation and combustion and the sand mould and cores are completely broken down to discrete sand particles, then depositing a combination of hot castings and hot, regenerated sand as resulting from said tumbling step into a second rotating vessel and tumbling such materials in that second vessel during a time period sufficient to ensure that the castings and sand are cooled down to ambiant temperature, and thereupon separating the resulting combination of castings and sand into its components.
 7. The process as claimed in claim 6, wherein the materials within said first vessel are passed through flames in order to ensure a complete combustion of synthetic resin.
 8. The process as claimed in claim 6, wherein an oxygen-containing gas is supplied to the materials within said first vessel to ensure a good combustion of synthetic resin.
 9. The process as claimed in claim 6, wherein any flue gases and water vapor resulting from combustion of synthetic resin are removed from said first vessel by suction.
 10. The process as claimed in claim 6, wherein the materials within said second vessel are tumbled under a water spray.
 11. The process as claimed in claim 6, wherein the materials within said second vessel are tumbled under a water spray and wherein said water spray has a slightly alkaline pH value for neutralising any phosphoric acid as present in said regenerated sand. 